Evidence for an extrarenal action of chlorothiazide on serum potassium.

The effects of chlorothiazide and furosemide on serum potassium were studied in fasting anuric patients maintained by chronic hemodialysis and compared to a control period when no drug was administered. Serum potassium levels were significantly lower following oral chlorothiazide (15 mg/kg body weight) than during the control period. After intravenous furosemide (1 mg/kg body weight), potassium levels were midway between those of the chlorothiazide and control periods, but statistical significance was not attained. Comparing the three study periods, there were no significant differences in the changes in body weight, blood pressure, blood pH, hematocrit, urea, glucose, sodium, albumin, insulin, plasma renin activity and aldosterone. This suggests that an extrarenal action of chlorothiazide on the cell membrane promotes cellular uptake of potassium.